fix: update remaining test assertions for Python 3.14 compatibility

- Add 3.14 to USING_COVERAGE in CI workflow
- Fix 5 additional output type assertions in TestSysExit and
  TestOutputFormatting that also use hard-coded output indices
- Use next() to find error outputs by type when accessing ename/evalue

Author: costajohnt

.github/workflows/ci.yml

@@ -12,7 +12,7 @@ jobs:
     name: "Python ${{ matrix.python-version }}"
     runs-on: "ubuntu-latest"
     env:
-      USING_COVERAGE: '3.10,3.11,3.12,3.13'
+      USING_COVERAGE: '3.10,3.11,3.12,3.13,3.14'
 
     strategy:
       fail-fast: false

papermill/tests/test_execute.py

@@ -283,9 +283,12 @@ def test_sys_exit(self):
         self.assertEqual(nb.cells[0].cell_type, "code")
         self.assertEqual(nb.cells[0].execution_count, 1)
         self.assertEqual(nb.cells[1].execution_count, 2)
-        self.assertEqual(nb.cells[1].outputs[0].output_type, 'error')
-        self.assertEqual(nb.cells[1].outputs[0].ename, 'SystemExit')
-        self.assertEqual(nb.cells[1].outputs[0].evalue, '')
+        # Python 3.14+ may emit a stderr stream before the error output
+        output_types = [o.output_type for o in nb.cells[1].outputs]
+        self.assertIn('error', output_types)
+        error_output = next(o for o in nb.cells[1].outputs if o.output_type == 'error')
+        self.assertEqual(error_output.ename, 'SystemExit')
+        self.assertEqual(error_output.evalue, '')
         self.assertEqual(nb.cells[2].execution_count, None)
 
     def test_sys_exit0(self):
@@ -296,9 +299,12 @@ def test_sys_exit0(self):
         self.assertEqual(nb.cells[0].cell_type, "code")
         self.assertEqual(nb.cells[0].execution_count, 1)
         self.assertEqual(nb.cells[1].execution_count, 2)
-        self.assertEqual(nb.cells[1].outputs[0].output_type, 'error')
-        self.assertEqual(nb.cells[1].outputs[0].ename, 'SystemExit')
-        self.assertEqual(nb.cells[1].outputs[0].evalue, '0')
+        # Python 3.14+ may emit a stderr stream before the error output
+        output_types = [o.output_type for o in nb.cells[1].outputs]
+        self.assertIn('error', output_types)
+        error_output = next(o for o in nb.cells[1].outputs if o.output_type == 'error')
+        self.assertEqual(error_output.ename, 'SystemExit')
+        self.assertEqual(error_output.evalue, '0')
         self.assertEqual(nb.cells[2].execution_count, None)
 
     def test_sys_exit1(self):
@@ -314,7 +320,9 @@ def test_sys_exit1(self):
         self.assertEqual(nb.cells[2].cell_type, "markdown")
         self.assertRegex(nb.cells[2].source, '<span id="papermill-error-cell" .*</span>')
         self.assertEqual(nb.cells[3].execution_count, 2)
-        self.assertEqual(nb.cells[3].outputs[0].output_type, 'error')
+        # Python 3.14+ may emit a stderr stream before the error output
+        output_types = [o.output_type for o in nb.cells[3].outputs]
+        self.assertIn('error', output_types)
 
         self.assertEqual(nb.cells[4].execution_count, None)
 
@@ -326,9 +334,12 @@ def test_system_exit(self):
         self.assertEqual(nb.cells[0].cell_type, "code")
         self.assertEqual(nb.cells[0].execution_count, 1)
         self.assertEqual(nb.cells[1].execution_count, 2)
-        self.assertEqual(nb.cells[1].outputs[0].output_type, 'error')
-        self.assertEqual(nb.cells[1].outputs[0].ename, 'SystemExit')
-        self.assertEqual(nb.cells[1].outputs[0].evalue, '')
+        # Python 3.14+ may emit a stderr stream before the error output
+        output_types = [o.output_type for o in nb.cells[1].outputs]
+        self.assertIn('error', output_types)
+        error_output = next(o for o in nb.cells[1].outputs if o.output_type == 'error')
+        self.assertEqual(error_output.ename, 'SystemExit')
+        self.assertEqual(error_output.evalue, '')
         self.assertEqual(nb.cells[2].execution_count, None)
 
     def test_line_magic_error(self):
@@ -460,6 +471,8 @@ def test_output_formatting(self):
         self.assertEqual(nb.cells[2].cell_type, "markdown")
         self.assertRegex(nb.cells[2].source, '<span id="papermill-error-cell" .*</span>')
         self.assertEqual(nb.cells[3].execution_count, 2)
-        self.assertEqual(nb.cells[3].outputs[0].output_type, 'error')
+        # Python 3.14+ may emit a stderr stream before the error output
+        output_types = [o.output_type for o in nb.cells[3].outputs]
+        self.assertIn('error', output_types)
 
         self.assertEqual(nb.cells[4].execution_count, None)